The context of my problem is:
I have a Windows .NET app (GUI) running as a main process.
From this (parent) process, I create a couple of sub-processes as console processes.
The main process sends data to the children processes through named pipes.
In the main app, I have a list of the sub-processes.
My probleme is that each console has a close ("x") button and can be terminated (whatever the way it is). Since I keep a list of the created consoles in my main app, I would like to know when a console is killed or exited.
My console (child process) program is simply a "main()" with a loop function that reads the pipe (and displays the data). It has no message system or whatever else that could handle a windowing "exit".
The first idea that comes to my head is to poll the sub-processes from the main app to refresh the list. But this means I have to introduce a timer or a thread that watches the consoles. I don't like the idea.
Does someone have a better idea?
WaitForSingleObject(hThread, 0) will tell you whether the thread specified in hThread argument is signaled and therefore finished. Same goes to hProcess.
Both handles of your child process are returned after CreateProcess() call. You can either close them immediately, or monitor using WaitForSingleObject.
Related
Usually when a program is run from the Windows console, the console will wait for the process to exit and then print the prompt and wait for user input. However, if the process starts a child process, the console will still only wait for the first process to exit. It will not wait for the child as well.
Is there a way for the program to get the console to wait on another child process instead of (or as well as) the current process.
I would assume it's impossible because presumably the console is waiting on the process' handle and there's no way to replace that handle. However, I'm struggling to find any confirmation of this.
Is there a way for the program to get the console to wait on another child process instead of (or as well as) the current process.
No. As you noted, as soon as the 1st process the console creates has exited, the console stops waiting. It has no concept of any child processes being created by that 1st process.
So, what you can do instead is either:
simply have the 1st process wait for any child process it creates before then exiting itself.
if that is not an option, then create a separate helper process that creates a Job Object and then starts the main process and assigns it to that job. Any child processes it creates will automatically be put into the same job as well 1. The helper process can then wait for all processes in the job to exit before then exiting itself. Then, you can have the console run and wait on the helper process rather than the main process.
1: by default - a process spawner can choose to break out a new child process from the current job, if the job is setup to allow that.
I am developing an application in windows which should run a code just before the process terminates. i am okay writing a kernel module to achieve this. but what are the functions that i should hook into ?
To get the notification about the termination of process i am doing this.
HANDLE handle = OpenProcess(PROCESS_ALL_ACCESS, FALSE, 1234);
DWORD wait = WaitForSingleObject(handle, INFINITE);
// Some block of code here that does the business logic.
handleProcessTermination();
My problem is the target process exits before my function handleProcessTermination() completes. i want a way to stop the exit of process and run my logic.
You should be able to create a kernel driver that calls PsSetCreateProcessNotifyRoutineEx to create a callback routine for when processes start/end. Your callback will be called "just before the last thread to exit the process is destroyed."
This won't allow you to "stop" the process termination permanently, but does allow you to inject some code just prior to the process ending.
I think there is no way to postpone the termination of a process. Even stopping all threads of that process will not help since the killing of the process is done by the kernel.
Due to my own experience I assume that windows does the following on process termination:
Mark the process to be terminated
Terminate all threads of the process
Clean up (free memory, release handles, ...)
Terminate process
Once step 1. is done the process is doomed since the scheduler will not activate any of the threads of that process. Activating one of the threads may cause them to go berserk since the process is in a partly destroyed state (e.g. memory may be freed, handles destroyed, ...) which may cause serious trouble!
I don't think that there is a possibility to change that behavior without chaning parts of the kernel.
Side note: It would be an interresting thing to test if WaitForSingleObject(thread, ...) is signalled before WaitForSingleObject(process, ...).
In Ruby, how do I ensure that child processes spawned from my program don't keep running when my main process exits or is killed?
Initially I thought I could just use at_exit in the main process, but that won't work if my main process gets kill -9ed or calls Kernel.exec. I need a solution that is (basically) foolproof, and cross-platform.
If you have to handle kill -9 termination for your parent app, then you have only a couple of choices that I can see:
Create a work queue manager and spawn/kill child processes from work queue manager. If you can't guarantee that the work queue manager won't also be killed without warning, then option 2 is your only choice I think, since the only thing you know for sure is that the child processes are still running.
http://www.celeryproject.org/
http://aws.amazon.com/elasticbeanstalk/
More aggressive approach - basically spawn off whole OS instances but they'll definitely get killed off within your parameters for operation
Have the child processes check a "heartbeat" from the parent process through RPC or monitoring parent PID in memory or watching a date/time on keep-alive file in /tmp to make sure it's current.
If the child processes fail to see the parent processes doing it's job of either responding to RPC messages, staying in memory itself, or keeping a file date/time current the child processes must kill themselves.
I am debugging a process on a web server running Linux. The process is invoked once a request is coming from a web-page. In order to debug the process, I look at the running processes list (using top), I spot the relevant process (named apache2) by it's CPU usage (quite easy, since it is usually on top of the list), and I attach the gdb session to the process id. Of course I can call the attach PID command only after the process is up.
The only problem is that this process-id-spotting takes a second or two, so I cannot stop at functions which are called during the first second or two. (The whole process takes about a minute so in most cases it is not a problem).
Is there any way of doing this automatically, so I can save these couple of seconds and start the attachment earlier?
You can attach to the parent process and catch forks. Don't forget to set follow-fork-mode child.
I know Windows close kernel handles when an application crashes, but if I want to wait on this event, can I be sure it will happen in milisec or it might take a while? I would like to trigger a new function the moment one application is crashed and I'm checking if this handle is NULL but it seems like I can't get a NULL value in this case.
How long it will take may vary depending upon many factors including implementation, type of crash, etc. It might take awhile.
If you want to know when a process has crashed, you should set up a "watchdog" thread or process that waits on the application's Process Handle, using a function such as WaitForSingleObject. When the process dies, the event will be signaled and you can act accordingly.
Windows does not close handles when an application "crashes" - it closes them when the process terminates, no matter how the process terminates. By the time this happens the variables don't exist any more because the user mode address space has been shut down.
What are you trying to do?